This invention relates to a device which measures an integrated intensity of the solar UV radiation responsible for erythema, and in particular to a pattern that relies on chemical changes that are caused by the radiation that is being measured, (that is, an Actinometer).
There are very many reasons for wanting to know the intensity of radiation that reaches the earth from the sun. The need can usually be allotted to one of two classes; for survey, to determine the relative or absolute intensity in a specific band of wavelengths and to compare the intensities at different times or places; and as a dosimeter, to determine whether or not, or when, a person or other sensitive object has had an assigned integrated dose. There have been many instruments that can be used in one or other of these classes, and it may be that the first class can be satisfied by a relatively small number of instruments for one survey, and is already well enough dealt with. For example, a survey was carried out to find what effect supersonic aircraft could have on the earth's climate by alterating the transmission of UV through the upper atmosphere. There is a longstanding belief that sunlight of the wavelengths that cause sunburn also is responsible for skin cancer, and that it would be be profitable to know the relative intensity of the appropriate radiation (which is in the UV) at different sites and especially in different countries. For these inquiries it has been common to use electronic meters which are expensive. Indeed, it is their cost which prevents their use in large numbers to monitor radiation at many locations for the average project.
Berger, Photochem. and Photobiol. Vol. 24, p. 587 (1976) says that for UV radiation measurements in the erythemal or sunburn range of wavelengths, there are four types of intensity meter--chemical, filter, photodiode and fluorescent--and that the drawbacks of the four types are respectively:
(1) chemical cannot measure variations with time,
(2) filters must be used with diffusers or collimators to see the whole sky, and so are insensitive,
(3) photodiodes have been found to be unstable,
(4) a fluorescent meter may have a spectrum that is not wanted.
The present meter is intended to work in the erythemal band and to integrate the received radiation with time. For this use, the disadvantage stated above for the chemical type does not apply.
World Health organization Environmental Health Criteria 14, says at p. 90:
"Measurement of solar UVR involves serious dificulties because of the need for accurate spectral discrimination at the shortest end of the solar spectrum. Few really practical, accurate, stray-light-free spectro-radiometers have been developed so far for use in the middle UVR region (UV-B). But if they can be perfected, such personal dosimeters would be of the greatest value."
Various erythemal UV actinometers (most are the subjects of patents) based on polysulphone films, aziridine compounds, solutions of triphenyltetrazolium chloride, 2-(2',4' dinitrobenzyl) pyridine, and 3'-[p-(dimethylamino)-phenyl]spiro-[fluorene-9,4'-oxazolidine]-2',5'-dione are known, but as erythemal monitors they are unsatisfactory, for their response spectra are not sufficiently close to that of the skin.
Another defect common to these actinometers is that they record by changes of colour, which are associated with changes to the wavelength dependences of their actinic responses.
The UV absorption spectrum of many disulphides is similar to the erythemal action spectrum. Further, it is known that principal products resulting from the absorption of UV radiation by a solution of a disulphide, in the absence of oxygen are thiols or sulphides, neither of which has UV absorptions which will alter the absorption spectrum of a partly photolyzed disulphide solution over the spectrum of solar radiation at the earth's surface, i.e., .gtoreq.295 nm.
The photolysis of disulphides in a low-temperature organic glass has been studied. Much of the photochemistry of this system results as a consequence of the very low temperatures used.
The photolysis of organic disulphides in fluid solution has also been studied, but until now, because of the solvents used, side photoreactions occur in addition to the formation of thiol. These side rections prohibit the use of these solutions as actinometers.